1a. Objectives (from AD-416):
The main focus of the work proposed here will be to use an evolutionary bioassay-driven process to make lab and then field-ready pheromone lures by starting with highly purified (LC/HPLC) pheromone components and formulate them on rubber septa and other lab substrates that have been de-activated (cleaned up/extracted); ratios of emitted pheromone volatiles will be assessed regularly. The pheromone components will be stabilized with BHT and Sumisorb™ and these lures will be compared to “standard” filter-paper sources and a commercial lure formulation from ISCA Technologies.
1b. Approach (from AD-416):
The approach will be to be as rigorous as possible with chemical purity, lure dosing and assessment of pheromone release ratios and then add a graded or stepwise level of “stress” on the pheromone formulations. Lures made with rubber septa have been known to be unstable with some aldehyde-containing pheromone blends. To circumvent this problem, we will exhaustively extract rubber septa, plastic vials and tubes with a Soxhlet device or by boiling them in hot solvents to remove compounds that can catalyze aldehyde pheromone degradation. These prospective lures with then be loaded with the now known 4-component pheromone blend and their by quality and longevity testing will start in the laboratory by comparison with filter paper disks loaded with gland extract or the 4-component pheromone blend as positive controls.
3. Progress Report:
This report deals specifically with Objective 2a to develop a stable formulation for the recently identified female sex pheromone of the navel orangeworm. The navel orangeworm (NOW) is well known as the primary lepidopteran pest of almonds and pistachios. NOW control is accomplished by removal of mummified nuts (orchard sanitation) plus insecticide sprays. Timing of insecticide sprays is and has long been determined by assessing NOW levels based on counts of NOW eggs on traps and nuts. It is hoped that monitoring NOW presence by trapping with the recently identified sex pheromone will be less labor intensive and a more accurate way to estimate NOW presence and numbers and thus a better tool for NOW management. In the current study, our approach to developing a field lure for monitoring NOW was to use purified pheromone components placed on “standard” commercial formulation materials that have been thoroughly cleaned by chemical means. An early field check of this approach was conducted 2 years ago and we found septa-based lures to be effective at trapping NOW for at least one week compared to female-baited traps. This work continued with different chemical extracts of the septa and different synthetic batches of pheromone, but we found no improvement in the one-week efficacy. We also continued work on volatile collections as we believe that will yield clues to why lures decline in effectiveness. Recently, we focused our efforts on volatile ratios emitted from female pheromone glands and lures to determine the optimal ratios for better and more consistent trapping. Collection of pheromone volatiles on open glass capillaries is efficient since all the adhered odor molecules can be stripped from the capillary wall by a relatively small volume of solvent. However, for the low levels of pheromone release for NOW we needed a more efficient tool. We have compared gas chromatography columns with glass capillaries and solid adsorbent traps to collect pheromone volatiles and have found the gas chromatography column to be very effective and uses much less solvent than the other trapping techniques allowing direct analyses of collected pheromone volatiles without sample "work up" that can lead to less accurate results. We are currently testing different gas chromatography column coatings and coating thicknesses for long term trapping of NOW pheromone volatiles. When it is completed, these methods will allow us to aid in the development of longer lasting field lures for navel orangeworm.